Fluidity of Al–Si semisolid slurries during rheocasting by a novel process

Lower fluidity of semisolid metallic slurries considerably limits their mold filling ability in rheocasting processes. In this paper, rheo-centrifuged casting (RCC) process was introduced and its performance was evaluated in terms of casting fluidity. Slurries were continuously cooled and stirred until reaching the desired fraction liquids up on which they were poured into a rotating sand mold. It was found that fluidity of Al–7.1 wt% Si semisolid slurry increased approximately linearly with the square of the initial fraction liquid. Casting fluidity also showed a relationship in the form of exp(nr) with section thickness of the channel (r). The exponent n appeared to be a function of the external force (centrifugal force) and was independent of fraction liquid. Casting fluidity was also found to increase with slurry stirring speed due to lower flow resistance resulted from smaller and more rounded primary particles formed. Some degree of liquid segregation was observed along the length of the mold channels which was more severe for smaller casting cross sections. In summary, RCC process was proved as a viable method for improving the casting fluidity of the alloy.